BF150 water in lower cylinder but good pressure and spark.

I have twin 2008 BF150s with low 320 hours, probably too low but it is what it is. Its a salt water dive boat in Key Largo Florida it only goes about 15 miles round trip to the reef. It's rinsed always after it's stored on its lift.

I was gone about 3 months and when I ran the boat for about 30 minutes one of the engines started running poorly and I shut it down and came back to dock on one engine.
I pulled out the plugs and found water in the lowest cylinder.
I checked water separator and no water was found.
I did a compression test on all cylinders and got 205,205,192,205 top to bottom. Pressure would hold in all four at those levels.

Once I dry out the cylinders and replace the plugs, they all get spark.
When I run the engine out of the water, all cylinders fire and the engine seem okay except cant run long because no cooling water.

As soon as I put the engine in the water and start it up the bottom cylinder gets water in it again and stops firing.

The analyzer returns no codes.

Could this be a problem with the exhaust manifold? Getting and holding pressure on all 4 seems to negate a head issue. Where can the water be coming from if not through exhaust somehow?

I am at the limit of my know how. I need some guidance before tearing this engine down.

The water will almost certainly be coming from a corroded cyl head. You will need to remove the head for inspection

That's planned but how is water getting into the cylinder but compression holding if there's a hole in it?

Post # 1 indicates you are running this motor out of water with no water supplied to cool the impeller.-----You now need to install a new impeller !!!

15 seconds max

Also due to be replaced anyway. Still wondering if could be exhaust manifold not head

Picking up on Racerone's comment - 3 seconds running without water will damage the impeller. Change it.

Sorry, disagree, those impellors are extremely robust. Anyway, I doubt exhaust has anything to do woth water in the cylinder, there will be corrosion causing the issue.

Do a leak down test on the wet cylinder. Start at TDC and, with the normal rotation direction of the engine, let the piston move down the bore with the air pressure. You will see if you have a corrosion leak.

If the engine spins in reverse while doing this test you will need to make sure the timing belt did not jump a tooth or few.

your cylinder head likely has a pin hole in it, from corrosion. this allows water from the coolant jacket to penetrate the cylinder

It's getting taken to the honda repair spot down here. When I have a final answer I will post it. I've had this problem before and it was the hole in the cyl. Seems odd that it would happen again in such a short time frame. Beginning to think about repower with Yamaha.